Fuel supply system for an internal combustion engine providing time and voltage compensated cranking enrichment

ABSTRACT

IN AN ELECTRONIC FUEL INJECTION SYSTEM, FUEL IS APPLIED TO AN INTERNAL COMBUSTION ENGINE FOR THE DURATION OF INDIVIDUAL CONTROL PULSES DEVELOPED IN SYNCHRONIZATION WITH THE ROTATION OF THE ENGINE. THE ENGINE STARTING SEQUENCE IS DIVIDED INTO ALTERNATE CRANKING PERIODS AND RESTING PERIODS. DURING EACH CRANKING PERIOD, ADDITIONAL CONTROL PULSES ARE SUPPLIED AT A FREQUENCY WHICH IS INVERSELY RELATED TO THE TEMPERATURE OF THE ENGINE AND WHICH IS ALSO INVERSELY RELATED TO THE SUPPLY VOLTAGE OF A POWER SOURCE. FURTHER, THE ADDITIONAL CONTROL PULSES ARE SUPPLIED ONLY DURING AN ENRICHMENT INTERVAL. THE MINIMU POSSIBLE DURATION OF THE ENRICHMENT INTERVAL IS DETERMINED AS A   DIRECT FUNCTION OF THE DURATION OF THE INSTANT CRANKING PERIOD. THE MAXIMUM POSSIBLE DURATION OF THE ENRICHMENT INTERVAL IS DETERMINED AS A DIRECT FUNCTION OF THE DURATION OF THE PREVIOUS RESTING PERIOD AND AS AN INVERSE FUNCTION OF THE DURATION OF THE PREVIOUS CRANKING PERIOD.

P. N. BARR 3,616,784 FUEL SUPPLY SYSTEM FOR AN INTERNAL COMBUSTION ENGINE PROVIDING TIME AND VOLTAGE COMPENSATED CRANKING ENRICHMENI' 5 Sheets-Sheet 1 Nov. 2, 1971 Filed July 1.7, 1970 1 W 0 i z WW W z 11} m C| I! w W I W J A I. ET M m W. WW y M Q W m a A MW J r Z; a Q 11 l/Fl l I l I I 1| 1 1 1 1| I1] I l .I lHv w p 5 U 7% mw M w w y w A W M w w A V a, m H 1 r. m 1 A 1 O 6% .1 WWW I Q 2 6 W I N 3 1 m m m w mu mmw U Z /w w 0 J A ATTORNEY Nov. 2, 1971 P. N. BARR 3,616,784

FUEL SUPPLY SYSTEM FOR AN INTERNAL COMBUSTION ENGINE PROVIDING TIME AND VOLTAGE COMPENSA'IED CRANKING ENRICHMENT Filed July 17, 1970 5 Sheets-Sheet 2 ATTORNEY 1971 P. N. BARR 3,616,784

FUEL SUPPLY SYSTEM FOR AN INTERNAL COMBUSTION ENGINE PROVIDING TIME AND VOLTAGE COMPENSATED CRANKING ENRICHMENT Filed July 17, 1970 3 Sheets-Sheet 8 nn nn m! n+1 ATTORNEY United States Patent 3,616,784 FUEL SUPPLY SYSTEM FOR AN INTERNAL COMBUSTION ENGINE PROVIDING TIME AND VOLTAGE COMPENSATED CRANK- ING ENRICHMENT Paul N. Barr, Kokomo, Ind., assignor to General Motors Corporation, Detroit, Mich.

Filed July 17, 1970, Ser. No. 55,630

Int. Cl. F02n 11/08 US. Cl. 123-179 G 4 Claims ABSTRACT OF THE DISCLOSURE In an electronic fuel injection system, fuel is applied to an internal combustion engine for the duration of individual control pulses developed in synchronization with the rotation of the engine. The engine starting sequence is divided into alternate cranking periods and resting periods. During each cranking period, additional control pulses are supplied at a frequency which is inversely related to the temperature of the engine and which is also inversely related to the supply voltage of a power source. Further, the additional control pulses are supplied only during an enrichment interval. The minimum possible duration of the enrichment interval is determined as a direct function of the duration of the instant cranking period. The maximum possible duration of the enrichment interval is determined as a direct function of the duration of the previous resting period and as an inverse function of the duration of the previous cranking period.

The present invention relates to a fuel supply system for an internal combustion engine. More particularly, the invention relates to an electronic fuel injection system for increasing the amount of fuel applied to an internal combustion engine during cranking.

The invention of the present application is related to improvements in the invention of application Ser. No. 44,988 filed June 10, 1970 in the names of John W. Moulds et al., which was filed previous to this application. The previous application is assigned to the assignee of the present application and the disclosure of the previous application is hereby incorporated with the present application.

According to the invention, an electronic fuel injection system applies fuel to an internal combustion engine for the duration of individual control pulses developed in synchronization with the rotation of the engine. The engine starting sequence is divided into alternate cranking periods and resting periods. During each cranking period, additional control pulses are supplied at a frequency which is inversely related to the temperature of the engine and which is also inversely related to the supply voltage of a power source. Further, the additional control pulses are supplied only during an enrichment interval. The minimum possible duration of the enrichment interval is determined as a direct function of the duration of the present cranking period. The maximum duration of the enrichment interval is determined as a direct function of the duration of the preceding resting period and as an inverse function of the duration of the previous cranking period in excess of the previous enrichment interval.

In a preferred embodiment of the invention, a starter circuit initiates cranking of the engine when manually actuated and tenninates cranking of the engine when manually deactuated. The starter circuit defines a cranking period when actuated and a resting period when deactuated. A cranking oscillator produces cranking pulses when enabled. A cranking timer includes a timer control circuit and a timer switching circuit. The timer switching circuit includes a bistable switch and a logic switch. The timer 3,616,784 Patented Nov. 2., 1971 control circuit develops a timer control voltage which varies with respect to a timer control level. The bistable switch assumes a set state when the timer control voltage decreases to the timer control level and assumes a reset state when the timer control voltage increases to the timer control level. The logic switch enables the cranking oscillator to produce cranking pulses during an enrichment interval extending from the time when the starter circuit is actuated until the earlier of the time when the starter switch is next deaotuated and the time when the timer control voltage next increases to the timer control level. A control pulse generator produces additional control pulses in response to the occurrence of each of the cranking pulses.

In the timer control circuit, the timer control voltage is defined across a capacitor. A charging circuit charges the capacitor at a charge rate when the starter circuit is actuated. A discharge circuit discharges the capacitor at a first discharge rate when the bistable switch is in the set state and at a second discharge rate when the bistable switch is in the reset state. The charge rate is greater than the first and second discharge rates. Accordingly, the timer control voltage increases during the cranking period at a first positive rate defined by the charge rate less the first discharge rate when below the timer control level and at a second positive rate defined by the charge rate less the second discharge rate when above the timer control level. Conversely, the timer control voltage decreases during the resting period at a first negative rate determined by the second discharge rate when above the timer control level and at a second negative rate determined by the first discharge rate when below the timer control level.

These and other aspects and advantages of the invention will become more apparent by reference to the following detailed description of a preferred embodiment when considered in conjunction with the accompanying drawing.

In the drawing:

FIG. 1 is a schematic diagram of an electronic fuel injection system incorporating the principles of the invention.

FIG. 2 is a schematic diagram of a cranking enrichment circuit incorporating the principles of the invention.

FIGS. 3, 4 and 5 are graphic diagrams of waveforms useful in explaining the principles of the invention.

Referring to FIG. 1, an internal combustion engine 10 for an automotive vehicle includes a combustion chamber or cylinder 12. A piston 14 is mounted for reciprocation within the cylinder 12. A crankshaft 16 is supported for rotation within the engine 10. A connecting rod 18 is pivotally connected between the piston 14 and the crankshaft 16 for rotating the crankshaft within the engine 10 when the piston 14 is reciprocated within the cylinder 12.

An intake manifold 20 is connected with the cylinder 12 through an intake port 22. An exhaust manifold 24 is connected with the cylinder 12 through an exhaust port 26. An intake valve 28 is slidably mounted within the top of the cylinder 12 in cooperation with the intake port 22 for regulating the entry of combustion ingredients into the cylinder 12 from the intake manifold 20. A spark plug 30 is mounted in the top of the cylinder 12 for igniting the combustion ingredients within the cylinder 12 when the spark plug 30 is energized. An exhaust valve 32 is slidably mounted in the top of the cylinder 12 in cooperation with the exhaust port 26 for regulating the exit of combustion products from the cylinder 12 into the exhaust manifold 24. The intake valve 28 and the exhaust valve 32 are driven through a suitable linkage 34 which conventionally includes rocker arms, lifters, and a camshaft.

An electrical power source is provided by the vehicle battery 36. An ignition switch 38 connects the battery 36 between a power line 40 and a ground line 42. When the ignition switch 38 is closed, the battery 36 applies a supply voltage to the power line 40. A conventional ignition circuit 44 is electrically connected to the power line 40 and is mechanically connected with the crankshaft 16 of the engine 10. Further, the ignition circuit 44 is connected through a spark cable 46 to the spark plug 30. In a conventional manner, the ignition circuit 44 energizes the spark plug 30 in synchronization with the rotation of the crankshaft 16 of the engine 10. Hence, the ignition circuit 44 combines with the ignition switch 38 and the spark plug 30 to form an ignition system.

A fuel injector 48 includes a housing 50 having a fixed metering orifice 52. A plunger 54 is supported within the housing 50 for reciprocation between a fully opened position and a fully closed position. In the fully opened position, the forward end of the plunger 54 is opened away from the orifice 52. In the fully closed position, the forward end of the plunger 54 is closed against the orifice 52. A bias spring 56 is seated between the rearward end of the plunger 54 and the housing 50 for normally maintaining the plunger 54 in the fully closed position. A solenoid or winding 58 is electromagnetically coupled with plunger 54 for driving the plunger 54 to the fully opened position against the action of the bias spring 56 when the winding 58 is energized. The bias spring 56 drives the plunger -4 to the fully closed position when the winding 58 is deenergized. The fuel injector 48 is mounted on the intake manifold 20 of the engine for injecting fuel into the intake manifold at a constant flow rate through the metering orifice 52 when the plunger 54 is in the fully opened position. Notwithstanding the illustrated structure, it is to be noted that the fuel injector 48 may be provided by virtually any suitable constant flow rate valve.

A fuel pump 60 is connected to the fuel injector 48 by a conduit 62 and to the vehicle fuel tank 64 by a conduit 66 for pumping fuel from the fuel tank 64 to the fuel injector 48. Preferably, the fuel pump 60 is connected to the power line to be electrically driven from the vehicle battery 36. Alternately, the fuel pump 60 could be connected to the crankshaft 16 to be mechanically driven from the engine 10. A pressure regulator 68 is connected to the conduit 62 by a conduit 70 and is connected to the fuel tank 64 by a conduit 72 for regulating the pressure of the fuel applied to the fuel injector 48. Thus, the fuel injector 48 combines with the fuel tank 64, the fuel pump 60 and the pressure regulator 68 to form a fuel supply system.

A throttle 74 is rotatably mounted within the intake manifold 20 for regulating the flow of air into the intake manifold 20 in accordance with the position of the throttle 74. The throttle 74 is connected through a suitable linkage 76 with the vehicle accelerator pedal 78. As the accelerator pedal 78 is depressed, the throttle 74 is opened to increase the flow of air into the intake manifold 20. Conversely, as the accelerator pedal 78 is released, the throttle 74 is closed to decrease the flow of air into the intake manifold 20.

In operation, fuel and air are combined within the intake manifold 20 to form an air/fuel mixture. The fuel is injected into the intake manifold 20 at a constant flow rate by the fuel injector 48 in response to energization. The precise amount of fuel deposited within the intake manifold 20 is regulated by a fuel supply control system which will be described later. The air enters the intake manifold 20 from the air intake system (not shown) which conventionally includes an air filter. The precise amount of air admitted into the intake manifold 28 determined by the position of the throttle 74. As previously described, the position of the accelerator pedal 78 controls the position of the throttle '74.

As the piston 14 initially moves downward within the cylinder 12 on the intake stroke, the intake valve 28 is opened away from the intake port 22 and the exhaust valve 32 is closed against the exhaust port 26. Accordingly, combustion ingredients in the form of the air/fuel mixture within the intake manifold 20 are drawn by negative pressure through the intake port 22 into the cylinder 12. As the piston 14 subsequently moves upward within the cylinder 12 on the compression stroke, the intake valve 28 is closed against the intake port 22 so that the air/fuel mixture is compressed between the top of the piston 14 and the top of the cylinder 12. When the piston 14 reaches the end of its upward travel on the compression stroke, the spark plug 30 is energized by the ignition circuit 44 to ignite the air/fuel mixture. The ignition of the air/fuel mixture starts a combustion reaction which drives the piston 14 downward within the cylinder 12 on the power stroke. As the piston 14 again moves upward within the cylinder 12 on the exhaust stroke, the exhaust valve 32 is opened away from the exhaust port 26. As a result, the combustion products in the form of various exhaust gases are pushed by positive pressure out of the cylinder 12 through the exhaust port 26 into the exhaust manifold 24. The exhaust gases pass out of the exhaust manifold 24 into the exhaust system (not shown) which conventionally includes a mufiler and an exhaust pipe.

Although the structure and operation of only a single combustion chamber of cylinder 12 has been described, it will be readily appreciated that the illustrated internal combustion engine 10 may include additional cylinders 12 as desired. Similarly, additional fuel injectors 48 may be provided as required. However, as long as the fuel injectors 48 are mounted on the intake manifold 20, the number of additional fuel injectors 48 need not necessarily bear any fixed relation to the number of additional cylinders l2. Alternately, the fuel injector 48 may be directly mounted on the cylinder 12 so as to inject fuel directly into the cylinder 12. In such instance, the number of additional fuel injectors 48 would necessarily equal the number of additional cylinders 12. At this point, it is to be understood that the illustrated internal combustion engine 10, together with all of its associated equipment, is shown only to facilitate a more complete understanding of the inventive fuel supply control system.

A timing pulse generator 80 is connected with the crankshaft 16 for developing timing pulses having a frequency which is proportional to and synchronized with the rotating speed of the crankshaft 16. The timing pulses are applied to a timing line 82. Preferably, the timing pulse generator 80 is some type of inductive speed transducer coupled with a bistable circuit. However, the timing pulse generator 80 may be provided by virtually any suitable pulse producing device such as a multiple contact rotary switch.

An injector drive circuit 84 is connected to the power line 40 and to the timing line 82. Further, the injector drive circuit 84 is connected through an injection line 86 to the fuel injector 48. The injector drive circuit 84 is responsive to the timing pulses produced by the timing pulse generator 80 to energize the fuel injector valve 48 in synchronization with the rotating speed of the crankshaft 16 in much the same manner as the ignition circuit 44 energizes the spark plug 30. The length of time for which the fuel injector 48 is energized by the drive circuit 84 is determined by the width or duration of the control pulses produced by a modulator or control pulse generator 88 which will be more fully described later. The control pulses are applied by the control pulse generator 88 to the injector drive circuit 84 over a control line 90 in synchronization with the timing pulses produced by the timing pulse generator 80. In other words, the injector drive circuit 84 is responsive to the coincidence of a timing pulse and a control pulse to energize the fuel injector 48 for the duration of width of the control pulse.

The injector drive circuit 84 may be virtually any amplifier circuit capable of logically executing the desired coincident pulse operation. However, where additional fuel injectors 48 are provided, it may be necessary that the injector drive circuit 84 also select which one or ones of the fuel injectors 48' are to be energized on each respective timing pulse. As an example, where the fuel injectors 48 are mounted on the intake manifold 20, they may be divided into two separate groups which are alternately energized on successive ones of the timing pulses. Conversely, where the fuel injectors 48 are mounted directly on additional cylinders 12, the timing pulses may be applied to operate a counter which individually selects the fuel injectors 48 for energization.

The control pulse generator 88 includes a monostable multivibrator or blocking oscillator 92. The blocking oscillator 92 includes a control transducer 94 having a primary winding 96 and a secondary winding 98 which are variably inductively coupled through a movable magnetizable core 100. The deeper the core 100 is inserted into the primary and secondary windings 96 and 98, the greater the inductive coupling between the primary winding 96 and the secondary winding 98. The movable core 100 is mechanically connected through a suitable linkage 102 withv a vacuum sensor 104. The vacuum sensor 104 communicates with the intake manifold 20 of the engine downstream from the throttle 74 through a conduit 106 for monitoring the negative pressure within the intake manifold 20. The vacuum sensor 104 moves the core 100 within the control transducer 94 to regulate the inductive coupling between the primary and secondary windings 96 and 98 as an inverse function of the vacuum within the intake manifold 20. Therefore, as the vacuum within the intake manifold decreases in response to the opening of the throttle 74, the core 100 is inserted deeper within the control transducer 94 to proportionately increase the inductive coupling between the primary Winding 96 and the secondary winding 98.

The monostable multivibrator or blocking oscillator 92 further includes a pair of NPN junction transistors 108 and 110. The primary winding 96 is connected from the collector electrode of the transistor 110 through a limiting resistor 112 to the power line 40. The secondary winding 98 is connected from an input junction 114 through a steering diode .116 to a bias junction 118 between a pair of biasing resistors 120 and 122 which are connected in series between the power line 40 and the ground line 42. A biasing resistor 124 is connected between the junction 114 and the power line 40. The base electrode of the transistor 108 is connected through a steering diode 126 to the junction 114. The emitter electrodes of the transistors 108 and 110 are connected directly to the ground line 42. The collector electrode of the transistor 108 is connected through a biasing resistor 128 to the power line 40 and is connected through a biasing resistor 130 to the base electrode of the transistor 110.

Further, the control pulse generator 88 includes a differentiator 132 provided by a capacitor .134 and a pair of resistors 136 and 138. The resistors 136 and 138 are connected in series between the power line 40 and the ground line 42. The capacitor 134 is connected from the timing line 82 to a junction 140 between the resistors 136 and 138. A steering diode 142 is connected from the junction 140 between the resistors 136 and 138 to the input junction 114. In operation, timing pulses are applied through the timing line 82 to the differenator 132. The differentiator 132 develops negative trigger pulses at the junction 140 in response to the timing pulses. The diode 142 applies the trigger pulses from the junction 140 to the junction 114.

The modulator or control pulse generator 88 is generally well known in the fuel injector art. Accordingly, since it is only incidental to the present invention, its operation will not be described in great detail. In opera tion, the monostable multivibrator or blocking oscillator 92 switches from a stable state to an unstable state in response to a decrease in the voltage at the input junction 114 below a predetermined threshold level. The voltage appearing at the junction 114 comprises a feedback voltage provided by the control transducer 94 and a bias voltage provided by the resistors 120, 122 and 124. Specifically, when the voltage at the junction 114 rises above the threshold level, the transistor 108 is rendered fully conductive through the coupling action of the diode 126 and the transistor is rendered fully nonconductive through the biasing action of the resistor 130.

-With the feedback voltage absent, the bias voltage provided by the resistors 120, 122 and 124 normally maintains the voltage at the junction 114 above the threshold voltage so that the transistor 108 is normally turned on and the transistor 110 is normally turned off. However, when a negative trigger pulse arrives at the junction 114, the voltage at the junction 114 immediately drops below the threshold level. Consequently, the transistor 108 is turned off through the coupling action of the diode 126, and the transistor 110 is turned on through the biasing action of the resistors 128 and 130. With the transistor 110 turned on, a control pulse is initiated on the control line 90. The level of the control pulse is defined by the saturation voltage drop of the transistor 110.

With the transistor 110 turned on, a current is established in the primary winding 96 of the control transducer 94 to develop the feedback voltage across the secondary winding 98 of the control transducer 94. The feedback voltage initially instantaneously decreases from the level of the bias voltage to a lower level and subsequently gradually increases back to the level of the bias voltage. The feedback voltage is coupled through the diode 116 to the junction 114 to hold the voltage at the junction 114 below the threshold level. Consequently, the transistor 108 remains turned off and the transistor 110 remains turned on.

The lower level of the feedback voltage is determined by the inductive coupling between the primary and sec ondary windings 96 and 98 of the control transducer 94. In turn, the inductive coupling between the primary and secondary windings 96 and 98 is defined by the position of the movable core 100. The rate at which the feedback voltage increases from the lower level back to the level of the bias voltage is determined by the L/R time constant of the primary Winding 96 and the limiting resistor 112. As the feedback voltage increases, the voltage at the junction 114 eventually rises above the threshold level. Accordingly, the transistor 108 is turned on and the transistor'110 is turned off. With the transistor 108 turned off, the control pulse on the control line 90 is terminated. Thus, the duration of the control pulses occurring on the control line 90 is determined by the vacuum sensor 104 and the control transducer 94 as an inverse function of the vacuum within the intake manifold 20 of the engine 10.

A starter circuit 146 is mechanically connected With the crankshaft 16 of the engine 10 through a suitable linkage 148. A starter switch 150 connects the vehicle battery 36 with the starter circuit 146 through a starting line 152. When the starter switch 150 is closed, the starter circuit 146 is actuated to initiate cranking of the engine 10. When the starter switch 150 is opened, the starter circuit .146 is deactuated to terminate cranking of the engine 10. Preferably, the starter switch 150 is ganged with the ignition switch 38 in the conventional manner. When ganged, the ignition switch 38 is closed when the starter switch 150 is in the starting position, but the starter switch 150 is opened when the ignition switch 38 is in the running position. Conventionally, the starter circuit 150 includes a starter solenoid and a starter motor. Thus, the starter circuit 146 combines with the starter switch 150 to form a starting system.

Duringcranking of the engine 10 by the starter circuit 146, the rotation of the crankshaft 16 is relatively slow. As a result, the frequency of the timing pulses produced by the timing pulse generator 80 is relatively low. Consequently, the frequency of the control pulses produced by the control pulse generator 88 is also low. With the number of control pulses reduced during cranking of the engine 10, the amount of fuel deposited within the intake manifold 20 by the fuel injector 48 is generally insufficient to insure reliable starting of the engine 10. In addition, when the engine is cold, some of the applied fuel tends to condense upon the walls of the intake manifold and upon the surface of the intake valve 28. As a result, the amount of fuel actually drawn from the intake manifold 20 through the intake port 22 past the intake valve 28 into the cylinder 12 is substantially reduced during cold cranking of the engine 10. For these reasons, a cranking enrichment circuit 154 is provided for increasing the number of control pulses developed by the control pulse generator 88 during cranking of the engine 10.

The cranking enrichment circuit 154 is connected between the power line 48 and the ground line 42. The cranking enrichment circuit 154 includes an input connected through the starting line 152 to the starter switch 150. Correspondingly, the cranking enrichment circuit 154 includes an output connected through an output line 156 to a differentiator 158 in the control pulse generator 88. The ditferentiator 158 is provided by a capacitor 160 and a pair of resistors 162 and 164. The resistors 162 and 164 are connected in series between the power line and the ground line 42. The capacitor 160 is connected between the output line 156 of the cranking enrichment circuit 154 and a junction 166 between the resistors 162 and 164. A steering diode 168 is connected from the junction 166 between the resistors 162 and 164 to the input junction 114 in the monostable multivibrator or blocking oscillator 92.

In a manner to be more fully described later, the cranking enrichment circuit 154 is responsive to cranking of the engine 10, When the starter switch 150 is closed to produce cranking pulses on the output line 156. The cranking pulses produced by the cranking enrichment circuit 154 are applied through the output line 156 to the differentiator 158. The differentiator 158 develops negative trigger pulses at the junction 166 in response to the cranking pulses. The diode 168 applies the trigger pulses from the junction 166 to the junction 114. As previously described, the monostable multivibrator or blocking oscillator 92 produces control pulses in response to the occur rence of the trigger pulses at the input junction 114. Hence, additional control pulses are developed by the control pulse generator 88 during cranking of the engine 10.

As might be expected, the total amount of fuel which is condensed upon the walls of the intake manifold 20 and upon the surface of the intake valve 28 is inversely related to the temperature of the engine 10. Therefore, as the engine temperature increases, an increasing amount of fuel is drawn from the intake manifold 20 through the intake port 22 past the intake valve 28 into the cylinder 12 tending to flood the engine 10 with excess fuel. Accordingly, the cranking enrichment circuit 154 includes an input connected through a sensing line 170 to a heat sensing element 172 mounted on the top of the cylinder 12 adjacent the intake valve 28 for monitoring the temperature of the engine 10. Alternately, it will be appreciated that the heat sensing element 172 could be located in some other convenient position, such as within the engine coolant system. Preferably, the heat sensing element 172 is provided by a negative temperature coefficient resistor or thermistor. The thermistor 1'72 regulates the frequency of the cranking pulses produced by the cranking enrichment circuit 154 as an inverse function of the temperature of the engine 10. Thus, the amount of fuel applied to the engine 10 during cranking is compensated for variations in the temperature of the engine 10.

In addition, if the energy capacity of the power source or battery 36 is relatively low, the supply voltage applied to the power line 40 and to the starting line 152 is de creased. As an example, the supply voltage of the battery 36 may be low due to an energy drain placed on the battery 36 by some external accessory equipment, such as the vehicle light system (not shown), When the engine 10 is shut off. With the supply voltage on the starting line 152 reduced, the speed at which the crankshaft 16 of the engine 10 is cranked by the starter circuit 146 is slowed.

Accordingly, the engine 10 is more difficult to start. Further, if the engine 10 does not rapidly start, the remaining energy of the battery 36 will be quickly depleted by the starter circuit 146 during cranking of the engine 10. In such event, it is impossible to start the engine 10.

Moreover, with the supply voltage on the power line 40 reduced, the magnitude of the voltage applied to the winding 58 of the fuel injector 48 by the injector drive circuit 84 is correspondingly lowered. Consequently, the response time of the fuel injector 48 is sluggish. More particularly, the opening time of the plunger 54 with respect to the metering orifice 52 is substantially increased. As a result, the amount of fuel deposited within the intake manifold 20 of the engine 10 by the fuel injector 48 is effectively decreased. Therefore, when the supply voltage of the battery 36 is low enough to adversely effect the response time of the fuel injector 48, the engine 10 is even more difficult to start. Further, since the amount of fuel deposited within the intake manifold 20 is inversely related to the temperature of the engine 10, engine starting is even more troublesome if the engine 10 is at an elevated tempearture when the supply voltage is reduced.

In order to alleviate these problems, the frequency of the cranking pulses produced by the cranking enrichment circuit 154 is regulated as an inverse function of the energy capacity of the power source of battery 36. More particularly, the frequency of the cranking pulses is increased by a given factor when the supply voltage of the battery 36 falls below a minimum acceptable level. Preferably, the frequency of the cranking pulses is doubled when the supply voltage is reduced. Thus, the amount of fuel applied to the engine 10 during cranking is compensated for variations in the supply voltage of the battery 36 as well as for variations in the temperature of the engine 10.

Ordinarily, the engine 10 will start quickl when cranked by the starter circuit 146. However, if the engine 10 initially fails to start, the starting sequence may become a series of alternate cranking periods and resting periods under control of the vehicle operator. A cranking period may be defined as that time interval during which the starter switch is closed to actuate the starter circuit 146. A resting period may be defined as that time interval during which the starter switch 150 is opened to deactuate the starter circuit 146.

As will be more fully described later, the cranking enrichment circuit 154 produces cranking pulses only during a limited enrichment interval. This prevents the engine 10 from becoming excessively flooded with fuel due to a continual supply of cranking pulses from the cranking enrichment circuit 154 in the absence of engine starting. Preferably, the enrichment interval begins when the starter switch 150 is closed to actuate the starter circuit 146 and initiate cranking of the engine 10. Similarly, the enrichment interval ends when the starter switch 150 is opened to deactuate the starter circuit 146 and terminate cranking of the engine 10. Hence, the minimum possible duration of an enrichment interval is directly related to the duration of the instant cranking period. This prevents the engine 10 from becoming flooded with fuel due to a continual supply of cranking pulses from the cranking enrichment circuit 154 in the absence of engine cranking.

Further, the maximum possible duration of an enrichment interval is directly related to the duration of the preceding resting period up to a predetermined limit. This prevents severe flooding of the engine 10 due to an excessive number of cranking pulses produced by the cranking emichment circuit 154 when the resting periods are disproportionately shorter than the cranking periods. In addition, the maximum possible duration of an enrichment interval is inversely related to the duration of the preceding cranking period up to a predetermined limit. More specifically, the maximum possible duration of an enrichment interval is inversely related to the duration of the preceding cranking period in excess of the preceding enrichment interval. This prevents continued flooding of the engine due to a constant oversupply of cranking pulses from the cranking enrichment circuit 154 when the successive cranking periods and resting periods occurred in rapid order after the engine 10 has been initially flooded.

Referring to FIG. 2, the cranking enrichment circuit 154 comprises a cranking oscillator 174 and a cranking timer 176. The cranking pulses generator or cranking oscillator 174 includes an oscillator switching circuit 178 and an oscillator control circuit 180. The oscillator switching circuit or oscillator toggle circuit 178 comprises a differential amplifier 182 and an output switch 184.

The differential amplifier 182 includes NPN junction transistors 186, 188, 200 and 202. The emitter electrode of the transistor 186 is connected through a biasing resistor 204 to the ground line 42. A voltage divider network includes a pair of biasing resistors 206 and 208 and a temperature compensating diode 210 which are connected in series between the power line 40 and the ground line 42. The base electrode of the transistor 186 is connected to a bias junction 212 between the resistor 206 and the diode 210. The collector electrode of the transistor 186 is connected directly to the emitter electrodes of the transistors 188 and 200. The base electrode of the transistor 188 is connected to the oscillator control circuit 180.

The collector electrode of the transistor 188 is connected throfigh a biasing resistor 214 to the power line 40. The collector electrode of the transistor 200 is connected through a temperature compensating diode 216 and a biasing resistor 218 to the power line 40. The base electrode of the transistor 202 is connected directly to the collector electrode of the transistor 188. The collector electrode of the transistor 202 is connected directly to the power line 40. The emitter electrode of the transistor 202 is connected through a pair of biasing resistors 220 and 222 to the ground line 42. The base electrode of the transistor 200 is connected to an oscillator reference junction or oscillator gating junction 224 between the resistors 220 and 222.

I The output switch 184 comprises a PNP junction translstor 226 and an NPN junction transistor 228. The base electrode of the transistor 226 is connected directly to the collector electrode of the transistor 200. The collector electrode of the transistor 226 is connected directly to the base electrode of the transistor 228. The emitter electrode of the transistor 226 and the collector electrode of the transistor 228 are connected together through an output resistor 230 to the power line 40. The emitter electrode of the transistor 228 is connected directly to the output line 156 of the cranking enrichment circuit 154.

The oscillator control circuit or oscillator integrator circuit 180 includes a storage element or capacitor 232, a charging circuit 234 and a discharging circuit 236. The discharging circuit 236 comprises a heat sensor network 238 and a voltage detector network 240. The capacitor 232 is connected between the base electrode of the transistor 188 and the ground line 42. An oscillator control junction 242 is defined between the top of the capacitor 232 and the base electrode of the transistor 188.

The charging circuit or current source 234 includes a PNP junction transistor 244 and an NPN junction transistor 246. The base electrode of the transistor 244 is connected directly to the collector electrode of the transistor 200. The emitter electrode of the transistor 244 and the collector electrode of the transistor 246 are connected through a charging resistor 248 to the power line 40. The

collector electrode of the transistor 244 and the base electrode of the transistor 246 are connected through a biasing resistor 250 to the oscillator control junction 242. The emitter electrode of the transistor 246 is connected directly to the oscillator control junction 242.

The discharging circuit or current sink 236 includes an NPN junction transistor 252. The collector electrode of the transistor 252 is connected directly to the oscillator control junction 242. The base electrode of the transistor 252 is connected with the heat sensor network 236. The emitter electrode of the transistor 252 is connected with the voltage detector network 240. Further, the emitter electrode of the transistor 252 is connected through a discharging resistor 254 to the ground line 42.

The heat sensor network 238 includes a pair of NPN junction transistors 256 and 258. The base electrode of the transistor 256 is connected to a junction between a pair of biasing resistors 260 and 262 which are connected in series between the power line 40 and the ground line 42. The collector electrode of the transistor 256 is connected directly to the power line 40. The base electrode of the transistor 258 is connected to a junction between the heat sensing element or thermistor 172 and a biasing resistor 263 which are connected in series between the emitter electrode of the transistor 256 and the ground line 42. The collector electrode of the transistor 258 is connected directly to the power line 40. The emitter electrode of the transistor 258 is connected through a pair of biasing resistors 264 and 266 to the ground line 42. The base electrode of the transistor 252 is connected directly to the junction between the resistors 264 and 266.

The voltage detector network 240 includes a pair of NPN junction transistors 268 and 270. The base electrode of the transistor 268 is connected to the junction between a pair of detecting resistors 272 and 274 which are connected in series between the power line 40 and the ground line 42. The emitter electrode of the transistor 268 is connected directly to the ground line 42. The collector electrode of the transistor 268 and the base electrode of the transistor 270 are connected together through a biasing resistor 276 to the power line 40. The emitter electrode of the transistor 270 is connected directly to the ground line 42. The collector electrode of the transistor 270 is connected through a discharging resistor 278 to the emitter electrode of the transistor 252.

The cranking timer 176 comprises a timer switching circuit 280 and a timer control circuit 282. The timer switching circuit or timer toggle circuit 280 includes a differential amplifier 284 and a logic switch 286. The differential amplifier 284 comprises NPN junction transistors 288, 290 and 292. The base electrode of the transistor 288 is connected directly to the bias junction 212 between the resistor 206 and the diode 210. The emitter electrode of the transistor 288 is connected through a biasing resistor 294 to the ground line 42. The collector electrode of the transistor 288 is connected directly to the emitter electrodes of the transistors 290 and 292.

A voltage regulator or voltage divider network is formed by a bias resistor 296 and a string of diodes 298, 300, 302 and 304 which are connected in series between the power line 40 and the ground line 42. The base electrode of the transistor 290 is connected to a timer reference junction 305 between the resistor 296 and the diode 298. The collector electrode of the transistor 290 is connected directly to the power line 40. The collector electrode of the transistor 292 is connected through a biasing resistor 306 to the power line 40. Thebase electrode of the transistor 292 is connected with the timer control circuit 282.

The logic switch 286 includes a PNP junction transistor 308 and an NPN junction transistor 310. The base electrode of the transistor 308 is connected directly to the collector electrode of the transistor 292. The emitter electrode of the transistor 308 is connected directly to the power line 40. The collector electrode of the transistor 308 is connected through a biasing resistor 312 to the base electrode of the transistor 310. The emitter electrode of the transistor 310 is connected directly to the ground line 42. The collector electrode of the transistor 310 is connected to the oscillator gating junction 224 between the resistors 220 and 222 in the oscillator switching circuiut 178.

The timer control circuit or timer integrator circuit 282 comprises a storage element or capacitor 314, a charging circuit 316 and a discharging circuit 318. The capacitor 314 is connected between the base electrode of the transistor 292 and the ground line 42. A timer control junction 320 is defined between the top of the capacitor 314 and the base electrode of the transistor 29-2. The discharging circuit or current sink 318 includes a discharging resistor 322 connected between the timer control junction 320 and the ground line 42. As will be more fully explained later, the discharging circuit 318 also includes the transistors 288 and 292 and the resistor 294 of the differential amplifier 284.

The charging circuit or current source 316 includes a PNP junction transistor 324 and a pair of NPN junction transistors 326 and 328. The base electrode of the transistor 324 is connected directly to the timer control junction 320. The emitter electrode of the transistor 324 and the collector electrode of the transistor 326 are connected together through a charging resistor 330 to the power line 40. The collector electrode of the transistor 324 and the base electrode of the transistor 326 are connected together through a biasing resistor 332 to the ground line 42. The emitter electrode of the transistor 326 is connected directly to the ground line 42. The collector electrode of the transistor 328 is connected directly to a timer gating junction 329 between the resistor 330, the emitter electrode of the transistor 324 and the col lector electrode of the transistor 326. The emitter electrode of the transistor 328 is connected directly to the ground line 42. The base electrode of the transistor 328 is connected through a pair of biasing resistors 334 and 336 to the power line 40. The base electrode of the transistor 310 is connected through a biasing resistor 338 and a turnoff diode 340 to an input junction 342 between the biasing resistors 334 and 336.

A cranking driver switch is provided by an NPN junction transistor 344. The collector electrode of the transistor 344 is connected directly to the input junction 342. The emitter electrode of the transistor 344 is connected directly to the power line 42. The base electrode of the transistor 344 is connected through a biasing resistor 346 to the starting line 152 and through a biasing resistor 348 to the ground line 42.

Referring to FIG. 2, when the starter switch 150- is opened to terminate cranking of the engine 10, the starting line 152 is deenergized. With the starting line 152 deenergized, the transistor 344 is rendered fully nonconductive through the biasing action of the resistor 348. With the transistor 344 turned ofi, the transistor 310 is rendered fully conductive through the biasing action of the resistors 336 and 338 and the diode 340. When the transistor 310 is turned on, the oscillator gating junction 224 is effectively clamped to the potential of the ground line 42. Consequently, the cranking oscillator 174 is disabled. However, when the starter switch 150 is closed to initiate cranking of the engine 10, the starting line 152 is energized. With the starting line 152 energized, the transistor 344 is rendered fully conductive through the biasing action of the resistors 346 and 348. With the transistor 344 turned on, the transistor 310 is rendered fully nonconductive through the biasing action of the resistor 338 and the diode 340. With the transistor 310 turned off, the oscillator gating junction 224 is unclamped. As a result, the cranking oscillator 174 is enabled.

Referring to FIGS. 2 and 3, when the cranking oscillator 174 is enabled, the oscillator control circuit 180 produces an oscillator control voltage V at the oscillator control junction 242. The oscillator control voltage V varies with respect to an upper oscillator control level 350 and a lower oscillator control level 352. In particular, the control voltage V increases at a positive excursion rate from the lower control level 352 to the upper control level 350. Alternately, the control voltage V decreases at a negative excursion rate from the uper control level 350 to the lower control level 352. The oscillator switching circuit 178 is responsive to the oscillator control voltage V to switch between a set state and a reset state. More specifically, the oscillator switching circuit 178 assumes the reset state when the control 'voltage V reaches the lower level 350 in the increasing sense. Conversely, the oscillator switching circuit 178 assumes the reset state when the control voltage V reaches the lower level 350 in the decreasing sense. A cranking pulse is produced on the output line 156 of the cranking enrichment circuit 154 each time the oscillator switching circuit 178 assumes the set state.

In the oscillator switching circuit 178, the differential amplifier 182 exhibits a high gain characteristic. The transistor 186 combines with the resistor 204 to provide a current sink for the transistors 188 and 200. The conduction of the transistor 186 is determined by the biasing action of the resistors 206 and 208 and the diode 210. The transistor 202 operates as an emitter-follower to define the upper and lower oscillator control levels 350 and 352 at the oscillator reference junction 224. When the oscillator switching circuit 178 is in the set state, the transistor 188 is turned on and the transistors 200, 226 and 228 are turned off. When the oscillator switching circuit 178 is in the reset state, the transistor 188 is turned OE and the transistors 200, 226 and 228 are turned on.

More particularly, as the oscillator control voltage V at the oscillator control junction 242 reaches the lower control level 352, the oscillator switching circiut 178 is driven to the reset state. As the oscillator switching circuit 178 assumes the reset state, the transistor 188 is rendered fully nonconductive and the transistor 200 is rendered fully conductive. With the transistor 1'88 turned oif, the transistor 202 is driven into relatively heavy conduction by the biasing action of resistor 214. Since the voltage drop across the transistor 202 is relatively low, the reference voltage established at the oscillator reference junction 224 is increased to approximately the upper oscillator control level 350. As the transistor 200 turns on, the oscillator control voltage V produced by the oscillator control circuit begins to increase toward the upper oscillator control level 350. Further, with the transistor 200 turned on, the transistors 226 and 228 in the output switch 184 are rendered fully conductive through the biasing action of the transistors 186 and 200, the resistors 204 and 21 8, and the diode 216. With the transistors 226 and 228 turned on, a relatively high voltage is applied through the resistor 230 to the output line 156.

As the oscillator control voltage V at the oscillator control junction 242 reaches the upper control level 350, the oscillator switching circuit 178 is driven to the reset state. As the oscillator switching circuit 178 assumes the reset state, the transistor 188 is rendered fully conductive and the transistor 200 is rendered fully nonconductive. With the transistor 188 turned on, the transistor 202 is driven into relatively light conduction by the biasing action of the transistors 186 and 188 and the resistors 204 and 214. Since the voltage drop across the transistor 202 is relatively high, the reference voltage established at the oscillator reference junction 224 is decreased to approximately the lower oscillator level 352. As the transistor 200 turns off, the oscillator control voltage V produced by the oscillator control circuit 180 begins to decrease toward the lower oscillator control level 352. Further, with the transistor 200 turned off, the transistors 226 and 228 in the output switch 184 are rendered fully nonconductive through the biasing action of the resistor 218 and the diode 216. With the transistors 226 and 228 turned otf,

13 a relatively low voltage is applied through the resistor 230 to the output line 156 to define a cranking pulse.

Thus, the oscillator switching circuit 178 produces cranking pulses on the output line 156 of the cranking enrichment circuit 154 in synchronization with the frequency of the oscillations in the oscillator control voltage V developed by the oscillator control circuit 180. More specifically, a cranking pulse is produced on the output line 156 each time the transistor 200 is turned off. In turn, the transistor 200 is turned off each time the oscillator control voltage reaches the upper oscillator control level 350. The frequency with which the oscillator control voltage V reaches the upper oscillator control level 350 is proportioned to the positive and negative excursion rates of the oscillator control voltage V Accordingly, the frequency of the cranking pulses produced on the output line 156 by the oscillator switching circuit 178 is also a direct function of the positive and negative excursion rates of the oscillator control voltage V In the oscillator control circuit 180, the capacitor 232 defines the oscillator control voltage V at the oscillator control junction 242. The charging circuit 234 applies a constant charging current to the capacitor 232 to charge the capacitor 232 at a constant charge rate when the oscillator switching circuit 178 is in the reset state. The discharging circuit 236 draws a constant discharging current from the capacitor 232 to discharge the capacitor 232 at a constant discharge rate when the oscillator switching circuit 178 is in both the set and reset states. In other words, the discharging circuit 236 operates independent of the operation of the oscillator switching circuit 178. The heat sensor network 238 regulates the discharge rate as an inverse function of the temperature of the engine 10. In addition, the voltage detector network 240 regulates the discharge rate as an inverse function of the supply voltage of the power source or battery 36.

The positive excursion rate of the oscillator control voltage V is determined by the charge rate less the discharge rate. Hence, the positive excursion rate of the control voltage V is a direct function of the temperature of the engine and the supply voltage of the battery 36. The negative excursion rate of the oscillator control voltage V is determined by the discharge rate only. Thus, the negative excursion rate of the control voltage V is determined by the discharge rate only. Thus, the negative excursion rate of the control voltage V is an inverse function of the temperature of the engine 10 and the supply voltage of the battery 36. The charge rate provided by the charging circuit 234 is substantially greater than the discharge rate provided by the discharging circuit 236. Preferably, the charge rate is several times greater than the discharge rate. Consequently, the discharge rate dominates the charge rate in determining the excursion time for one complete cycle of the oscillator control voltage V between the upper and lower oscillator control levels 350 and 352. More specifically, the frequency of the oscillations in the oscillator control voltage V is inversely related to the temperature of the engine 10 and the supply voltage of the battery 36. Therefore, the frequency of the cranking pulses produced on the output line 156 by the oscillator switching circuit 178 is also an inverse function of the temperature of the engine 10 and the supply voltage of the battery 36.

In the charging circuit 234, the transistors 244 and 246 are operated in a constant current mode to linearly charge the capacitor 232. The charge rate is determined by the charging current applied through a charge path including the resistor 248 and the transistor 246. The magnitude of the charging current may be regulated by varying either one or both of the resistors 248 and 250. When the transistor 200 is turned on as the oscillator switching circuit assumes the reset state, the transistors 244 and 246 are rendered conductive through the biasing action of the transistors 186 and 200, the resistors 204 and 218 and the diode 216. Accordingly, the application of the charging current to the capacitor 232 is initiated. When the transistor 200 is turned off as the oscillator switching circuit 178 assumes the set state, the transistors 244 and 246 are rendered fully nonconductive through the biasing action of the resistor 218 and the diode 216. Consequently, the application of the charging current to the capacitor 232 is terminated.

In the discharging circuit 236, the transistor 252 is operated in a constant current mode to linearly discharge the capacitor 232. The discharge rate is determined by the discharging current drawn from the capacitor 232 through a discharge path including the transistor 252 and the resistor 254. When the oscillator switching circuit 178 is in the reset state, the capacitor 232 also discharges somewhat through a discharge path including the baseemitter junction of the transistor 188, the transistor 186 and the resistor 204. However, the amount of discharging current drawn through the discharge path internal to the differential amplifier 182 is negligible as compared to the amount of discharging current drawn through the discharge path external to the differential amplifier 182. The magnitude of the discharging current is directly related to the magnitude of a bias voltage applied to the base electrode of the transistor 252 by the heat sensor network 238. Further, the magnitude of the discharging current is inversely related to the magnitude of a resistance applied between the emitter electrode of the transistor 252 and the ground line 42 by the voltage detector network 240.

In the heat sensor network 238, the transistors 256 and 258 are operated as emitter-followers. The conduction of the transistor 256 is determined by the biasing action of the resistors 260 and 262. The conduction of the transistor 258 is determined by the biasing action of the thermistor 172 and the resistor 263 in conjunction with the internal resistance of the transistor 256. Similarly, the voltage at the base electrode of the transistor 252 is determined by the biasing action of the resistors 264 and 266 in conjunction with the internal resistance of the transistor 258. As the temperature of the engine 10 increases, the resistance of the negative temperature coefficient thermistor 172 decreases so as to decrease the conduction of the transistor 258. However, as the conduction of the transistor 258 decreases, the voltage at the base electrode of the transistor 252 decreases so as to decrease the bias voltage applied to the base electrode of the transistor 252. As a result, the magnitude of the discharging current drawn through the transistor 252 and the resistor 254 decreases as the temperature of the engine 10 increases. Thus, the discharge rate of the capacitor 232 is inversely related to the temperature of the engine 10.

In the voltage detector network 240, the transistors 268 and 270 are operated as electronic switches. The supply voltage of the battery 36 appears across the power line 40 and the ground line 42. The detecting resistors 272 and 274 are selected to sense the level of the supply voltage with respect to a minimum acceptable level. When the supply voltage of the battery 36 is above the minimum acceptable level, the transistor 268 is rendered fully conductive through the biasing action of the resistors 272 and 274. With the transistor 268 turned on, the transistor 270 is rendered fully nonconductive. With the transistor 270 turned off, the voltage at the emitter electrode of the transistor 252 is defined by the biasing action of the resistor 254.

When the supply voltage of the battery 36 falls below the minimum acceptable level, the transistor 268 is rendered fully nonconductive through the biasing action of the resistors 2.72 and 274. With the transistor 268 turned off, the transistor 270 is rendered fully conductive through the biasing action of the resistor 276. With the transistor 270 turned on, the resistor 1278 is effectively placed in parallel with the resistor 254 to decrease the effective resistance between the emitter electrode of the transistor 252 and the ground line 42. Accordingly, the magnitude of the discharge current drawn through the transistor 252 increases when the supply voltage of the battery 36 falls below the minimum acceptable level. Hence, the discharge rate of the capacitor 232 is inversely related to the supply voltage of the battery 36.

Referring to FIG. 2, when the starter switch 150 is opened, the transistor 344 is rendered fully nonconductive. With the transistor 344 turned off, the transistor 328 is rendered fully conductive through the biasing action of the resistors 334 and 336. When the transistor 328 is turned on, the timer gating junction 329 is clamped to the potential of the ground line 42. Consequently, the cranking timer 176 is disabled. However, when the starter switch 150 is closed, the transistor 344 is rendered fully conductive through the biasing action of the resistors 346 and 348. With the transistor 344 turned on, the transistor 328 is rendered fully nonconductive through the biasing action of the resistor 334. When the transistor 328 is turned off, the timer gating junction 329 is unclamped. As a result, the cranking timer 176 is enabled.

Referring to FIGS. 3, 4 and 5, when the cranking timer 176 is enabled, the timer control circuit 282. produces a timer control voltage V at the timer control junction 320. The timer control voltage V varies with respect to a timer control level 3 54. The timer switching circuit 280 is responsive to the timer control voltage V, to switch between a set state and a reset state. The timer switching circuit 280 assumes the set state when the control voltage V, decreases below the timer control level 354 and assumes the reset state when the timer control voltage V increases about the timer control level 354.

In the timer switching circuit 280, the diflerential amplifier 284 exhibits a high gain characteristic. The transistor 2*8-8 combines with the resistor 294 to provide a current sink for the transistors 2'90 and 292. The conduction of the transistor 12 88 is determined by the biasing action of the resistors 2.06 and 8- and the diode 210. The voltage regulator or voltage divider formed by the resistor 296 in conjunction with the diodes 298, 300, 302 and 304 establishes a timer reference voltage at the timer reference junction 305. The timer reference voltage is fixed at approximately the timer control level 354. When the timer switching circuit 280 is in the set state, the transistor 2912' is turned off and the transistors 290 and 308 are turned on. When the timer switching circuit 280 is in the reset state, the transistor 292 is turned on and the transistors 290 and 308 are turned off.

More specifically, as the time control voltage V, at the timer control junction 320 decreases below the timer control level 354, the timer switching circuit 280 is driven to the set state. As the timer switching circuit 280 assumes the set state, the transistor 1290 is rendered fully conductive and the transistor 292 is rendered fully nonconductive. When the transistor 292 turns off, the transistor 308 in the logic switch 286 is rendered fully nonconductive through the biasing action of the resistor 306. As the timer control voltage V, at the timer control junction 320 increases above the timer control level 354, the timer switching circuit 280 is driven to the reset state. As the timer switching circuit 280 assumes the reset state, the transistor 290 is rendered fully nonconductive and the transistor 292 is rendered fully conductive. With the transistor 292 turned on, the transistor in the logic switch 286 is turned on through the biasing action of the transistors 288 and 292 and the resistors 294 and 306.

The transistor 31.0 operates to enable the cranking oscillator 174 when rendered fully nonconductive and to disable the cranking oscillator 174 when rendered fully conductive. Regardless of the operating condition of the transistor 1308, the transistor 310 is turned on through the biasing action of the resistors 336 and 338 and the diode 340 when the transistor 344 is turned off. Similarly, regardless of the operating condition of the transistor 344, the transistor 310 is turned on through the biasing action of the resistor 312 when the transistor 308 is turned on. The transistor 344 is turned on when the starter switch is closed and is turned oil when the starter switch 150 is opened. The transistor 30% is turned off when the timer switching circuit 280 is in the set state and is turned on when the timer switching circuit 280 is in the reset state. More particularly, the transistor 308 is turned on when the timer control voltage V decreases to the timer control level 354 and is turned olf when the timer control voltage V increases to the timer control level 354. Hence, the transistor 310 is turned ofl? to enable the cranking oscillator 174 when the starter switch 150 is closed and the timer control voltage V is below the timer control level 354. Further, the transistor 31!) is turned on to disable the cranking oscillator 174 when the starter switch 150 is opened or when the timer control voltage V is above the timer control level 354.

It will now be apparent that a cranking period may be defined to extend from the time when the starter switch 150 is closed until the time when the starter switch 150 is next opened. Similarly, a resting period may be defined to extend from the time when the starter switch 150 is opened until the time when the starter switch 150 is next closed. In addition, a set interval may be defined as extending from the time when the starter switch 150 is closed until the earlier of the time when the timer control voltage V, next reaches the timer control level 354 or the time when the starter switch 150 is next opened. Correspondingly, a reset interval may be defined as extending from the time when the starter switch 150 is opened until the earlier of the time when the timer control voltage V, next reaches the timer control level 354 or the time when the starter switch 150 is next closed. Further, since the cranking oscillator 174 produces cranking pulses on the output line 156 of the cranking enrichment circuit 154 only during the set interval, the set interval represents an enrichment interval. Hence, the timer switching circuit is in an enabled condition during an enrichment interval and is in a disabled condition at all other times.

In the timer control circuit 282, the capacitor 314 defines the timer control voltage V at the timer control junction 320. The charging circuit 316 applies a charging current to the capacitor 314 to charge the capacitor 314 only when the transistor 328 is turned oil. The discharging circuit 318 draws a discharging current from the capacitor 314 to discharge the capacitor 314 when the transistor 328 is both turned on and turned off. In other words, the operation of the discharging circuit 318 is independent of the operation of the transistor 328.

In the charging circuit 316, the transistors 324 and 326 are rendered fully conductive when the transistor 328 is turned off as the starter switch 150 is closed. Conversely, the transistors 324 and 326 are rendered fully nonconductive when the transistor 328 is turned on as the starter switch 150 is opened. When the transistors 324 and 326 are turned on, the capacitor 314 charges at a charge rate through a charging path including the base-emitter junction of the transistor 324 and the resistor 330. The charge rate is determined by the RC charging time constant provided by the capacitor 314 in conjunction with the resistor 330 and the effective base-emitter junction resistance of the transistor 324. Preferably, the RC charging time constant is chosen so that the charge rate as defined by the charging current applied through the charging path is substantially linear.

In the discharging circuit 318, the capacitor 314 is discharged at different first and second discharge rates. With the transistor 292 turned off when the timer switching circuit 280 is in the reset state, the capacitor 314 discharges at a first discharge rate through a first discharging path consisting of the resistor 322. The first discharge rate is determined by the RC time constant provided by the capacitor 314 in conjunction with the resistor 322. With the transistor 292 turned on when the timer switching circuit 280 is in the set state, the capacitor 314 discharges at a second discharge rate through the first discharge path including the resistor 322 and also through a second discharge path including the base-emitter junction of the transistor 292, the transistor 288 and the resistor 294. The second discharge rate is determined by the RC discharging time constant provided by the capacitor 314 in conjunction with the resistors 294 and 322, the base-emitter junction resistance of the transistor 292 and the internal resistance of the transistor 288.

Preferably, the RC discharging time constants are chosen so that the first and second discharge rates are substantially linear. The charge rate provided by the charging circuit 316 is substantially greater than the discharge rate provided by the discharging circuit 318. Further, the second discharge rate is substantially greater than the first discharge rate. In addition, it will be noted that the first discharge path is external to the differential amplifier 284 and the second discharge path is internal to the differential amplifier 284.

FIG. 4 depicts the excursion of the timer control voltage V over a complete operating cycle of the cranking timer 174. At time T the starter switch 150 is closed to actuate the starter circuit 146 and initiate cranking of the engine 10. As a result, the transistor 344 is turned on. Assuming the capacitor 314 became fully charged at time T the timer control voltage V, is at a minimum level below the timer control level 354. Accordingly, the transistor 290 is turned on and the transistors 292 and 308 are turned off. Since the transistor 344 is turned on and the transistor 308 is turned off, the transistor 310 is turned off. With the transistor 310 turned off, the cranking oscillator 174 is enabled to initiate the production of cranking pulses on the output line 156.

During the time interval T T the timer control voltage V increases at a first positive excursion rate de fined by the charge rate less the first discharge rate. At time T the timer control voltage V, reaches the timer control level 354 in an increasing sense. Consequently, the transistor 290 is turned otf and the transistors 292 and 308 are turned on. The transistor 344 remains turned on. Since the transistor 308 is turned on, the transistor 310 is turned on. With the transistor 310 turned on, the cranking oscillator 174 is disabled to terminate the production of cranking pulses on the output line 156.

Throughout the time interval T T the timer control voltage V, increases at a second positive excursion rate defined by the charge rate less the second discharge rate. The second positive excursion rate is less than the first positive excursion rate. At time T the timer control voltage V reaches a maximum level as the capacitor 314 becomes fully charged. During the time interval T -T the timer control voltage V remains constant at the maximum level. In the illustrated timer control circuit 282, the maximum level is the voltage level on the power line 40.

At time T the starter switch 150 is opened to deactuate the starter circuit 146 and terminate cranking of the engine 10. Consequently, the transistor 344 is turned 01f. However, since the transistor 308 remains turned on, the transistor 310 remains turned on. During the time interval T -T the timer control voltage V decreases at a first negative excursion rate defined by the second discharge rate. At time T the timer control voltage reaches the timer control level 354 in a decreasing sense. As a result, the transistor 290 is turned on and the transistors 292 and 308 are turned off. However, since the transistor 344 is turned off, the transistor 310 remains turned on. With the transistor 310 turned on, the cranking oscillator 17 4 remains disabled.

Throughout the time interval L -T the timer control voltage V decreases at a second negative excursion rate as defined by the first discharge rate. The second negative excursion rate is less than the first negative excursion rate. At time T the timer control voltage V reaches the minimum level as the capacitor 314 becomes fully discharged. During the time interval L -T the timer control voltage V remains at the minimum level. In the illustrated timer control circuit 282, the minimum level is the voltage level on the ground line 42. At time T the starter switch is again closed to actuate the starter circuit 146 and initiate cranking of the engine 10. Accordingly, the previously described cycle is repeated.

Although only the operating cycle T --T H is shown in its entirety, it is to be noted that there exists a preceding operating cycle T --T and a succeeding operating cycle T -T It will be recognized that the time interval T on represents a full cranking period and the time interval T -T +1 represents a full resting period. In addition, a maximum set interval or enrichment interval is represented by the time interval T -T and a maximum reset interval is represented by the time interval T -T The maximum possible duration of the set interval or enrichment interval T -T is a direct function of the duration of the preceding period T -T up to a predetermined limit defined by a maximum efiective resting interval T T Alternately, the maximum possible duration of the reset interval T -T is an inverse function of the duration of the preceding cranking period T -T up to a predetermined limit defined by a maximum effective cranking interval T -T More specifically, the maximum possible duration of the reset interval T -T is inversely related to the duration of the preceding cranking period T -T in excess of the duration of the preceding set interval or enrichment interval T -T Of course, it will be appreciated that the time T when the starter switch 150 is opened, can occur anytime after the time T when the starter switch 150 is closed. The time T marks the termination of the cranking period T -T and the initiation of the resting period T -T As the time T moves toward the time T the following reset interval is represented by the time interval T -T which remains unchanged at a maximum interval. As the time T moves away from the time T toward the time T the following reset interval is represented by the time interval T -T which proportionately decreases. As the time T moves away from the time T toward the time T the reset interval is nonexistent. Hence, as previously described, the duration of a reset interval is inversely related to the duration of the previous cranking period. Further, as the time T moves away from the time T toward the time T the set interval or enrichment interval is represented by the time interval T -T which proportionately decreases. Thus, the minimum possible duration of a set interval or enrichment interval is a direct function of the duration of the present cranking period.

Similarly, the time T when the starter switch 150 is closed can occur anytime after the time T when the starter switch 150 is opened. The time Tcn+1 marks the termination of the resting period T -T and the initiation of the cranking period T --T As the time Tcn+1 moves toward the time T the following set interval or enrichment interval is represented by the time interval T -T which remains unchanged at a maximum interval. As the time T, moves away from the time T toward the time T the following set interval or enrichment interval is represented by the time interval T -T which proportionately decreases. As the time T +1 moves away from the time T toward the time T the following set interval or enrichment interval is nonexistent. Thus, the duration of a set interval or enrichment interval is directly related to the duration of the previous resting period. Further, as the time Tcn+1 moves away from the time T toward the time T the reset interval is represented by the time interval T -T +1 which proportionately decreases. Hence, the minimum possible duration of a reset interval is a direct function of the duration of the present resting period.

FIG. depicts the excursion of the timer control voltage V during a hypothetical portion of an engine starting sequence which illustrates the previously described operation of the cranking enrichment circuit 154. During the first cranking period T -T the set interval is represented by the time interval T T Throughout the first resting period T -T the reset interval is nonexistent. Over the second cranking period T -T the set interval or enrichment interval is represented by the time interval T T During the second resting time period T -T the reset interval is represented by the time interval T -T Over the third cranking period T -T theset interval or enrichment interval is represented by the t1me interval T -T During the third resting period T -T the reset interval is represented by the time interval T T Throughout, the fourth cranking interval T T the set interval or enrichment interval is nonexistent. During the fourth resting period T T the reset interval is represented by the time interval T -T Referring to FIGS. 2 and 4, the maximum duration of the set interval or enrichment interval T -T may be adjusted by changing the first positive excursion rate of the timer control voltage V Similarly, the maximum duration of the reset interval T -T may be adjusted by changing the first negative excursion rate. Further, both the maximum duration of the set interval or enrichment interval T -T and the maximum duration of the reset interval T -T may be altered by changing the timer control level 354. Preferably, the maximum duration of the set interval or enrichment interval T -T is selected so that the engine becomes flooded with excess fuel just prior to the time T In addition, the maximum effective resting interval T -T is preferably substantially longer than the maximum effective cranking interval T -T As applied to a typical eight cylinder interval combustion engine, the following values for the respective time intervals were found to yield satisfactory results:

Time intervals: Seconds Maximum set interval or enrichment interval (Ten-n) 3 Maximum effective cranking interval (T -T 6 Maximum reset interval (T -T Maximum effective resting interval (T -T 30 It will now be apparent that the present invention provides an electronic fuel injection system having a cranking enrichment circuit which is both time compensated and voltage compensated. However, it is to be understood that the previous embodiment of the invention is shown for illustrative purposes onl and that various modifications and alterations may be made to it Without departing from the spirit and scope of the invention. As an example, the cranking pulses produced by the cranking enrichment circuit154 could be applied through an appropriate drive circuit to directly energize an extra fuel injector mounted on the intake manifold upstream of the fuel injector 48. Further, it is to be noted that the waveforms illustrated in the drawing are not necessarily to scale.

What is claimed is:

1. In an internal combustion engine system, the combination comprising: starter means connected with the engine for initiating cranking of the engine when actuated and for terminating cranking of the engine when deactuated, the starter means defining a cranking period when actuated and defining a resting period when deactuated; cranking timer means connected with the starter means, the cranking timer means including timer control means for developing a timer control voltage which varies with respect to a timer control level, the timer control voltage increasing during the cranking period at a first positive rate when below the timer control level and at a second positive rate when above the timer control level, and the timer control voltage decreasing during the resting period at a first negative rate when above the timer control level and at a second negative rate when below the timer control level, the cranking timer means further including timer switching means connected with the timer control means for defining an enrichment interval extending from the time when the starter means is actuated until the earlier of the time when the starter means is deactuated and the time when the timer control voltage increases to the timer control level, the enrichment interval thereby having a minimum possible duration determined as a direct function of the duration of the present cranking period and having a maximum possible duration determined as a direct function of the duration of the previous resting period and as an inverse function of the duration of the previous cranking period in excess of the. previous enrichment interval; and means including fuel injection means connected between the timer switching means and the engine for applying extra fuel to the engine only during the enrichment interval thereby to facilitate engine starting.

2. In an internal combustion engine system, the combination comprising: starter means connected with the engine for operation from a deactuated condition to an actuated condition to crank the engine, the starter means defining a cranking period while in the actuated condition and defining a resting period while in the deactuated condition; timing pulse generating means connected with the engine for producing timing pulses in synchronization with the rotation of the engine; cranking pulse generating means for producing cranking pulses when enabled; cranking timer means connected with the starter means, the cranking timer means including timer control means for develop ing a timer control voltage which varies with respect to a timer control level, the timer control voltage increasing during the cranking period at a first positive rate when below the timer control level and at a second positive rate when above the timer control level, and the timer control voltage decreasing during the resting period at a first negative rate when above the timer control level and at a second negative rate when below the timer control level, the cranking timer means further including timer switching means connected with the timer control means for enabling the cranking pulse generating means during an enrichment interval extending from the time when the starter means is actuated until the earlier of the time when the starter means is deactuated and the time when the timer control voltage increases to the timer control level, the enrichment interval thereby having a minimum possible duration determined as a direct function of the duration of the present cranking period and having a maximum possible duration determined as a direct function of the duration of the previous resting period and as an inverse function of the duration of the previous cranking period in excess of the previous enrichment interval; control pulse generating means connected with the timing pulse generating means and with the cranking pulse generating means for producing control pulses in response to the occurrence of each of the timing pulses and the cranking pulses, the control pulse generating means including transducer means connected with the engine for determining the duration of the control pulses as a function of at least one engine operating parameter; and means including fuel injection means connected between the control pulse generating means and the engine for injecting fuel into the engine at a substantially constant rate for the duration of each of the control pulses thereby to facilitate engine starting.

3. In an internal combustion engine system, the combination comprising: starter means connected with the engine for initiating cranking of the engine when manually actuated and for terminating cranking of the engine when manually deactuated, the starter means defining a cranking period when actuated and defining a resting period when deactuated; cranking oscillator means for producing cranking pulses when enabled; cranking timer means connected with the starter means, the cranking timer means including timer control means and timer switching means, the timer switching means including differential amplifier means for switching to a set state when a timer control voltage decreases below the timer control level and for switching to a reset state when the timer control voltage increases above the timer control level, the timer control means including a capacitor for defining the timer control voltage thereacross, charging means connected to the capacitor for charging the capacitor when the starter means is actuated at a charge rate through a charge circuit including the base-emitter junction of a transistor, discharging means connected between the capacitor and the differential amplifier means for discharging the capacitor at a first discharge rate which is less than the charge rate through a discharge path excluding the diiferential amplifier means when the differential amplifier means is in the set state and for discharging the capacitor at a second discharge rate which is less than the charge rate through a discharge path including the difierential amplifier means when the differential amplifier means is in the reset state, the timer control voltage thereby increasing during the cranking period when below the timer control level at a first positive rate defined by the charge rate less the first discharge rate and when above the timer control level at a second positive rate defined by the charge rate less the second discharge rate, and the timer control voltage thereby decreasing during the resting period when above the timer control level at a first negative rate defined by the second discharge rate and when below the timer control level at a second negative rate defined by the first discharge rate, and the timer switching means further including logic switching means connected between the cranking oscillator means and the capacitor for enabling the cranking oscillator means during an enrichment interval extending from the time when the starter means is actuated until the earlier of the time when the starter means is deacuated and the time when the timer control voltage increases above the timer control level, the enrichment interval thereby having a minimum possible duration determined as a direct function of the duration of the present cranking period and having a maximum possible duration determined as a direct function of the duration of the previous resting period and as an inverse function of the duration of the previous cranking period in excess of the previous enrichment interval; and means including fuel injection means connected between the cranking oscillator means and the engine for applying fuel to the engine at a sub stantially constant rate for a predetermined time period in response to each of the cranking pulses thereby to facilitate engine starting.

4. In an internal combustion engine system, the combination comprising: starter means connected with the engine for initiating cranking of the engine when manually actuated and for terminating cranking of the engine when manually deactuated, the starter means defining a cranking period when actuated and defining a resting period when deactuated; cranking timer means connected with the starter means, the cranking timer means including timer control means and timer switching means, the timer switching means including bistable means for assuming a set state when a timer control voltage decreases to a timer control level and for assuming a reset state when the timer control voltage increases to the timer control level, the timer control means including a capacitor for developing the timer control voltage thereacross, charging means connected to the capacitor for charging the capacitor at a charge rate when the starter means is actuated, and discharging means connected to the capacitor for discharging the capacitor at a first discharge rate which is substantially less than the charge rate when the bistable means is in the set state and at a second discharge rate which is substantially less than the charge rate when the bistable means is in the reset state, the timer control voltage thereby increasing duringthe cranking period when below the timer control level at a first positive rate defined by the charge rate less the first discharge rate and when above the timer control level at a second positive rate defined by the charge rate less the second discharge rate, and the timer control voltage thereby decreasing during the resting period when above the timer control level at a first negative rate defined by the second discharge rate and when below the timer control level at a second negative rate defined by the first discharge rate, and the timer switching means further including logic means connected with the capacitor for defining an enrichment interval extending from the time when the starter means is actuated until the earlier of the time when the starter means is deactuated and the time when the timer control voltage increases to the timer con trol level, the enrichment interval thereby having a minimum possible duration determined as a direct function of the duration of the present cranking period and having a maximum possible duration determined as a direct function of the duration of the previous resting period and as an inverse function of the duration of the previous cranking period in excess of the previous enrichment interval; and means including fuel injection means connected between the timer switching means and the engine for applying extra fuel to the engine only during the enrichment interval thereby to facilitate engine starting.

References Cited UNITED STATES PATENTS LAURENCE M. GOODRIDGE, Primary Examiner US. Cl. X.R. 12332 EA, 119

g UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 5l6 784 Dated govember 2 1971 lnven Paul N. Barr It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 11:

1 Column 3, line 71, after 20" insert is line 7,

line 7, "circuiut" should be circuit Column 12, "uper" should be upper line 11, "reset" should be set line 12, delete "lower" and insert upper control line 36, "circiut" should be circuit Column 13, line 43, delete "Thus, the negative excursion rate of the control voltage V is determined by the discharge rate only". Column 15, line 32, "about" should be above Column 18, line 19, after "preceding" insert resting Signed and sealed this 6th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOT'I'SCHALK Attesting Officer Commissioner of Patents 

